Nanoparticles, Nanosponges, Methods of Synthesis, and Methods of Use

ABSTRACT

Disclosed are novel metallic nanoparticles coated with a thin protective carbon shell, and three-dimensional nano-metallic sponges; methods of preparation of the nanoparticles; and uses for these novel materials, including wood preservation, strengthening of polymer and fiber/polymer building materials, and catalysis.

This application is a divisional of application Ser. No. 14/475,759,filed Sep. 3, 2014, now U.S. Pat. No. 9,574,136; which was acontinuation of application Ser. No. 13/249,558, filed Sep. 30, 2011,now U.S. Pat. No. 8,828,485; which was a divisional of application Ser.No. 12/278,295, filed Aug. 5, 2008, now abandoned; which was thenational stage of international application PCT/US2007/061862,international filing date Feb. 8, 2007; which claimed the benefit of theFeb. 10, 2006 filing date of provisional application Ser. No. 60/772,325under 35 U.S.C. §119(e). The complete disclosures of each of thesepriority applications are hereby incorporated by reference in theirentirety.

TECHNICAL FIELD

This invention pertains to metal-core carbon-shell nanoparticles(“MCCSNPs”) and nano-metallic Sponges, methods of making MCCSNPs andnano-metallic sponges, and methods for using MCCSNPs, for example, inthe protection of wood and in the strengthening of polymers andcomposites.

BACKGROUND ART

Metallic Nanoparticles and Methods for Generating

Nanomaterials offer unique properties (e.g., magnetic, optical,mechanical, and electronic) that vary with changes in particle size.Metal-based nanoparticles such as Au, Pt, Cu, and Ag, and metallicoxides, for example, FeO_(x)O_(y) have been used as industrialchemicals, catalysts, optical media, magnetic storage materials,materials for enhancing magnetic resonance imaging (MRI), and electrodematerials.

However, metallic nanoparticles without a protective coating often havea high propensity to oxidize or undergo other chemical reactions.Metal-core carbon-shell nanoparticles (sometimes referred to as“carbon-encased metal nanoparticles”), which have a metallic coresurrounded by a carbon shell, can broaden the uses of metallicnanoparticles. The metal in such nanoparticles is protected againstchemical reactions, and the carbon shells may be functionalized to havespecific physical, chemical, and biological properties.

Currently, synthesis of metal-core carbon-shell nanoparticles is basedon wet chemical or expensive physical methods that would be difficult toscale for commercial applications. The common techniques to make theseand other types of nanoparticles are described below.

Metal Evaporation is a simple way to fabricate metal/metal oxidenanoparticles. A mixture of a metal and its oxide is placed in a basketor pouch through which an electrical current is passed. This processcauses the metal and its oxide first to melt and then to vaporize. Anelectron beam may be used to assist in vaporizing metal/metal-oxidemixtures having high melting temperatures. Vaporization may occur eitherin vacuum or in an inert gas. Vaporized metal/metal-oxides aresolidified directly on a substrate placed above the basket or pouch. Thesize and size distribution of such particles depend on a number ofparameters including whether they are generated in an inert gas orvacuum, and if in a vacuum, the pressure. Metallic nanoparticlesproduced by this method tend to be very reactive, which is useful forsome applications but undesirable for others.

Sonochemical processing is a method for generating nanoparticles in anultrasonicated solvent. Sonochemistry involves acoustic cavitation,which appears to be caused by an implosive collapse of a bubble in anultrasonically irradiated liquid. This process generates a transient,localized hot spot with an effective temperature of about 5000° K atpressures of about 1000 atm. Heating and cooling rates may be greaterthan 1000° K/s. Acoustically cavitated bubbles produce large pressurevariations and fluid motion. In addition, there may be othersonochemical effects, such as momentum and mass transport, generation ofradicals and other excited particles, formation of high velocity liquidjets, and generation of shockwaves external to the bubble. Whilemetallic nanoparticles may be made by this method, the process isdifficult to control.

Chemical Reduction of metal ions in solution may be used to formmetallic nanoparticles. This process begins with a solution of a metalion. A reducing agent added to the solution causes precipitation of themetal, metal alloys, or metal carbides. Poly-alcohols, such as ethyleneglycol or diethylene glycol, have been used as both solvent andreductant. Particle size of precipitants depends on the rate ofnucleation and growth, and may be affected by aggregation during growth.This method has been used to form Au, Cu, Te, and Pt nanocrystallinemetals, and nanocrystalline intermetallics.

Protective Layers. Because of their high surface area-to-volume ratio,many metallic nanoparticles, including copper nanoparticles, are proneto readily oxidize or otherwise chemically react. To avoid this problema protective layer may be formed around the nanoparticles. Severaltechniques, such as layer-by-layer assembly, formation of microemulsion,modifications of the Kratschmer-Huffman carbon are method, hydrocarbondecomposition, arc discharge in de-ionized water, hydrolysis oftetraethoxysilicate (TEOS), plasma polymerization, plasma torchsynthesis, and flow-levitation have been used to coat metallicnanoparticles. Some of the more common methods are described below.

Layer-by-Layer Assembly (LBL) is a method for fabrication of compositenanomaterial films. This method is based on the sequential adsorption ofsubstrates in solutions of oppositely charged compounds. Nanometer filmthicknesses are typical. Deposition is controlled by adjustingprocessing conditions, such as solution pH, ionic strength, andimmersion time.

Microemulsion is a method in which two or more immiscible substances aredispersed. This dispersion or mixture typically contains water, oil, asurfactant, and sometimes a co-surfactant. An oil-in-water (O/W)microemulsion is one in which oil is at a droplet center surrounded bysurfactant and co-surfactant. A water-in-oil (W/O) microemulsion is onein which water is at a droplet center surrounded by oil. Thesubmicroscopic droplets/micelles may take up solutes and often exhibitdifferent environments than exhibited by bulk solvents. Microemulsiondroplets have been used to encapsulate water-soluble agents such asnanoparticles and submicron particles.

Kratschmer-Huffman Carbon Arc is a method originally used to makefullerenes. The method uses graphite rod electrodes to produce acontinuous DC electric arc discharge in vacuum. Carbon that evaporatesfrom an anode produces carbon soot. In high vacuum, the method producesa hard, graphite-like substance, while at lower vacuum it forms a finesoot rich in fullerenes and other nano-materials. This method has beenmodified by simultaneously evaporating carbon and a metal to generatenanoparticles comprising a carbonaceous material that encapsulates ametal nanoparticle. However, it appears that this process often resultsin the metal being oxidized.

Typically the existing methods for generating core-shell or coated metalnanoparticles are either too selective or too difficult to implement.For example, the LBL method has been reported to date to be limited topolymer and coated noble metal nanoparticles.

The microemulsion method cannot be applied generally because it requiresvery specific recipes for each metal salt. Further this method islimited by the reducing potential of the metal salt. In addition,nanoparticles generated by the microemulsion method tend to agglomerate.Further, like the LBL method, this method has been reported to date onlyto produce polymer or coated noble metal nanoparticles.

While the Kratschmer-Huffman carbon arc method appears to produce highquality carbon shells on metal particle surfaces, it also producesnumerous by-products, nanoparticles with large variations in shape andsize, and some metal oxides.

In addition, none of the existing methods for generating metallicnanoparticles routinely achieve complete carbon coating which providecomplete protection of metallic nanoparticles. The metallicnanoparticles tend to oxidize readily in air from the exposed surfaces,resulting in a short shelf-life for these materials unless stored underan inert gas. Scaled-up production using any of these methods also willbe difficult and expensive, because precise control of the methodvariables is difficult.

-   J. He et al., “Facile synthesis of noble metal nanoparticles in    porous cellulose fibers,” Chem. Mater., vol. 15, pp.    4401-4406 (2003) reported in situ, wet-chemistry formation of Ag,    Au, Pt, or Pd nanoparticles in porous cellulose fibers from the    corresponding noble metal salt precursors, using a traditional    reducing agent (NaBH₄). This method was not reported to produce a    carbon shell.-   J. He et al., “Facile fabrication of composites of platinum    nanoparticles and amorphous carbon films by catalyzed carbonization    of cellulose fibers,” Chem. Commun., Issue 4, pp. 410-411 (2004)    reported carbonizing cellulose matrixes containing reduced platinum    nanoparticles. J. He et al proposed that the platinum nanoparticles    may have catalyzed the carbonization of the cellulose matrix. The    resulting product consisted primarily of amorphous carbon fibers and    Pt nanoparticles.

H. Zhu et al., “Synthesis of assembled copper nanoparticles fromcopper-chelating glycolipid nanotubes,” Chem. Phys. Lett., vol. 405, pp.49-52 (2005) reported an annealing process for assembling coppernanoparticles from copper-chelating amphiphiles using glycolipidnanotubes.

Raymond et al, “In-Situ Synthesis of Ferrites in Cellulosics,” Chem.Mater. 6:249-255 (1994) disclosed that nano-ferrite particles could begenerated within a cellulosic matrix. This method appears to use anion-exchange mechanism to retain these particles within the cellulosicmatrix. No carbonization of this material was reported.

There exists an unfilled need for metallic nanoparticles that are stablein air and water, while still exhibiting desirable chemical activity,and a method of generating such metallic nanoparticles that is costefficient and scalable for industrial use.

Wood Preservation

Millions of homes are constructed each year from light frames made ofwood. Wood, unless protected, is naturally degraded by heat, moisture,insects, decay, mold and other forces. Formosan subterranean termites(Coptotermes formosanus) can be particularly destructive to wood.

It is well known that copper is a very effective wood preservative. Inrecent years, primarily because of environmental concerns, the mostwidely used form of copper, chromated copper arsenate (“CCA”), has beensubstantially reduced. Removal of CCA from the market has made woodpreservation more difficult.

Laks et al, U.S. Pat. No. 6,753,035 disclosed a method for incorporatingadditives such as biocides into wood or wood products using polymericnanoparticles.

Richardson et al, PCT Application WO 2006/065684 disclosed methods forprotecting wood against insect attack and decay by injecting sparinglysoluble copper hydroxide-containing particles into wood and woodproducts. This disclosure taught the use of micron size particles, andsuggested that particles smaller than 0.02 microns would tend to convertfrom metallic copper to copper oxide and be easily flushed from thewood.

Copper-containing wood preservatives that have been proposed to replaceCCA typically use one or more soluble copper ions (e.g., Cu⁺⁺). Coppercomplexes such as copper alkanolamine complexes, copper polyasparticacid complexes, alkaline copper quaternary salts, ammoniacal copperquaternary salts, ammoniacal copper zinc salts, copper azole, copperboron azole, copper bis-(dimethyldithiocarbamate), ammoniacal coppercitrate, copper citrate, and copper alkanolamine carbonate complexeshave been suggested. However, due primarily to cost, the onlyformulations that have been used commercially are copper alkanolaminecomplexes and copper ammonium complexes.

Wood is naturally resistant to mildews and certain molds, in partbecause there is very little fixed nitrogen in wood. However, amine andammonium complexes that add nitrogen to the wood may paradoxicallypromote mildew or mold. For example, amine and ammonium copper complexesappear to facilitate increased sapstain mold formation and enhancedmildew formation.

Another problem with commercially available copper-based preservativesis that they tend to be water-soluble, making them subject to leachingfrom wood exposed to moisture. To maintain protective amounts of copperin wood, a higher concentration of copper may need to be impregnatedinto the wood. While such an approach does not prevent leaching, it doesincrease the time during which the copper is effective. However, sincethe copper ions are thought to be toxic to aquatic life, such anincrease in the copper loading is not desirable because of theassociated increase in copper ions discharged into the environment. Inaddition, increasing the amount of copper increases the cost of thisprocess. Also, because amine and ammonium complexes may emit vapors,large amounts of these complexes of copper tend to increase the odor andirritation from the amine and ammonia fumes.

Another problem with existing commercial, copper-containing woodpreservatives is that they often cause corrosion of metal fasteners andother hardware. Metal ions as well as amines, alkanolamines, and ammoniaused in soluble copper treatments appear to contribute to corrosion ofmetal hardware. Thus, commercial copper-based wood preservative may notbe suitable for outdoor wooden structures, unless galvanized metal orstainless steel is used for all fittings. Use of such hardware will makethe wooden structure more costly.

An unfilled need exists for copper-containing wood preservatives thatare economical, that do not readily leach, that do not emit noxiousvapors, and that do not cause corrosion of fasteners.

Strengthening Polymer and Polymer Composite Materials

Polymers offer many advantages over conventional building materialsincluding lightness, resistance to corrosion and ease of processing.Polymers may be used alone or in combination with fibrous materials. Inaddition, polymers may be used as additives to form composites, whichmay be used as structural members. Polymer composites can be used inmany different forms ranging from structural composites in theconstruction industry to the high technology composites of the aerospaceand space satellite industries.

In recent years, composites comprising natural fibers, for example wood,and reinforced plastic have become one of the most rapidly growingmarkets within the polymer industry. In some markets more than 80% ofproducts such as decking, railing, windows, door profiles, and shinglesare either polymeric or fiber/polymer composites. Other uses of thesematerials include infrastructure, for example boardwalks, docks, andrelated structures, in the transportation industry, in automobiles, forexample interior panels, rear shelves, and spare tire covers, and withinthe industrial/consumer industry, for example picnic tables, parkbenches, pallets, and other similar products.

However, some concerns over product quality and product toughnessremain. Using wood or other natural fiber as filler in compositesincreases composite stiffness, but appears to reduce the toughness ofthe composite. Brittleness appears to be caused in part by stressconcentrations at fiber ends and by poor interfacial adhesion.

Thus an unfilled need exists for new additive or coupling agents forcomposites that improve toughness while maintaining or improving othercomposite properties.

SUMMARY OF THE INVENTION Novel Material

Metal-Core Carbon-Shell Nanoparticles

We have discovered nano-metallic materials coated with a thin carbonlayer. Prototypes have been made with metallic particle sizes less than10 μm, and preferably less than 50 nm, and more preferably less than 10nm, wherein the metal typically exists in a zero oxidation state. In oneembodiment, nano-size metal particles are completely coated with aprotective carbon shell, wherein said carbon shell has a thickness ofless than 20 nm, and preferably less than 10 nm, and more preferablyless than 1 nm, and more preferably less than 0.5 nm. Further saidparticles, when completely coated with carbon shells, are stable againstoxidation. In the special case of carbon-encased noble metals, the metalcore is resistant to attack by reagents that will otherwise dissolve orreact with such metals, for example aqua regia.

We have also discovered a novel process for making these nano-metallic,carbon-coated particles. This process comprises loading metal ions intofibers of biological origin, and then carbonizing the fibers. While notwishing to be bound by this theory, it appears that the metal ions arereduced into metal nanoparticle cores at natural interstices or othernanostructures in the natural fibers. The metals are reduced intonanoparticle cores, and carbon shells are formed around the cores,more-or-less simultaneously when the metal-ion impregnated naturalfibers are heated. In one embodiment, the carbonizing temperature issufficient to form a thin carbon shell encasing a metal nanoparticle.The carbonization temperature will differ for different metals and fordifferent fibers.

Natural biological systems often exhibit highly controlled and organizedstructures. The unique microstructures found in natural biologicalsystem may provide templates for producing metallic nanomaterials withina carbon shell. The process of making nanoparticles and nanoscalematerials using biological molecules through physical and chemicalmethods has been reported in the past. However, synthesizingnano-structures and materials, especially the core-shell structurenanoparticles, using natural fiber bio-templates from a carbonizationprocess has never been previously reported

Depending on the respective oxidation potentials and kinetics, theformation of core/shell nanoparticles for some metals may benefit by thepresence of an additional reducing agent in the reaction, e.g., hydrogengas, methane, thiosulfate, ferrous ion, borohydride, oxalic acid, orstannous ion. An additional reducing agent, aside from the natural fiberitself, was not found to be necessary for prototype demonstrations withcopper, silver, nickel, and gadolinium.

The invention may be practiced with naturally-occurring plant fibers oranimal fibers that have micro-pore structures. Plant fibers are based oncellulose, with or without the presence of lignin or hemilignin.Representative plant fibers include cotton, flax, linen, jute, ramie,sisal, hemp, milkweed, straw, bagasse, hardwoods, and softwoods. Animalfibers are largely based on proteins, for example, silk, hair, wool,spider silk, silkworm silk, sinew, and catgut.

Ions of metals, in addition to Cu, Ag, Ni, and Gd, may also be used. Forexample, the invention may be practiced with Group IIA metals (Be, Mg,Ca, Sr, Ba, Ra); Group IIIA metals or semi-metals (B, Al, Ga, In, Tl);Group IVA metals or semimetals (Si, Ge, Sn, Pb); Group VA metals orsemi-metals (As, Sb, Bi); Group VIA semi-metals (Te, Po); Group IIIBmetals (Sc, Y, La, Ac); Group IVB metals (Ti, Zr, Hf): Group VB metals(V, Nb, Ta); Group VIB metals (Cr, Mo, W); Group VIIB metals (Mn, Tc,Re); Group VIII metals (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt); Group IBmetals (Cu, Ag, Au); Group IIB metals (Zn, Cd, Hg); Lanthanides (Ce, Pr,Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu); and Actinides (Th, Pa,U, Np, Pu, Am). Further, mixtures of metals may be used.

Without wishing to be bound by this hypothesis, it is believed that thethree-dimensional structure of the native fiber provides a framework ortemplate for seeding the nascent nanoparticles, as well as providing thecarbon that will form the shell. Semi-synthetic derivatives of nativefibers can in some cases sufficiently preserve the framework, thetemplate, and accordingly may be used in this invention. For example,rayon, which is derived from cellulose, has been successfully used inpreparing copper/carbon core/shell nanoparticles in accordance with thisinvention. By contrast, totally synthetic fibers (e.g., nylon) have not,to date, been successful when used in an otherwise similar process.Without wishing to be bound by this theory, we believe that this may bebecause totally synthetic fibers generally lack the complexthree-dimensional framework or template that is characteristic of nativefibers, and that provide seeding loci for the formation of metallicnanoparticles.

Aqueous, non-aqueous, or mixed solvents may be used in practicing theinvention. The principal requirement of the solvent is that it shoulddissolve the metal ion being used. In general, distilled water is apreferred solvent, but other solvents may also be used. Examples of suchsolvents include methanol, ethanol, other alcohols, DMSO, DMF,hexamethylphosphorotriamide, formic acid, acetic acid, formic acid,acetone, and acetonitrile.

The novel core/shell nanoparticles were dispersible in both water andorganic solvents (such as oil). They were produced at a very low cost,and the encased metal was stable in air or water for months, withoutoxidation or other chemical reaction.

In one prototype embodiment, Cu⁺² ions were impregnated into cottonfiber (which contains naturally occurring cellulose, (C₆H₁₀O₅)_(n));extra solvent was removed from the impregnated fiber and then carbonizedat about 350° C. for about 2 hours. The resulting material containedcopper-core-carbon-shell nanoparticles (CCCSNPs).

Nano-Metallic Sponges

Alternatively the present invention may be used to makethree-dimensional nano-metallic sponges. The process is generallysimilar to that for making the core/carbon shell nanoparticles, but themetal ion-impregnated natural fibers are heated to a higher temperature,to a point where carbon is vaporized, and the metal nanoparticles juststart to sinter and connect to one another to form nano-spongestructures. The fiber skeleton acts as a frame/template to maketube-like nano-sponges, which have a far greater active surfacearea/volume ratio than most prior high surface area metallic structures.Previous catalyst structures using nanoparticles have generallysupported those nanoparticles on a matrix to enhance surfacearea/volume. But the prior structures are mainly two-dimensional becausethe nanoparticles rest on a generally inactive matrix material thatblocks some of the nanoparticle surface. Many commercial catalysts areshipped with protective compounds, and are activated on-site before use.For nano-sponge structures made in accordance with the presentinvention, after sintering without exposure to air, the sponge is nearlypure metal. Upon exposure to air, a metal oxide may be formed.

For example, prototype nano-metallic sponges have been made by soakingnatural fibers in a metal ion solution as previously described, followedby carbonizing the impregnated fibers at elevated temperature in aninert atmosphere (or under vacuum). A somewhat higher temperature isused to form nano-metallic sponges than the core/shell nanoparticles.For example, we have found that for copper a preferred temperature forforming core/shell nanoparticles is about 350° C., and a preferredtemperature for forming nano-metallic sponges is about 450° C. Forsilver, the corresponding temperatures are about 180° C. and about 280°C., respectively.

Without wishing to be bound by this hypothesis, it is believed thatcore-shell nanoparticles are formed throughout the entire carbonizedfiber skeleton first, as an intermediate step in the formation ofnano-metallic sponges. The carbonized fiber skeleton structure acts as atemplate for the formation of the sponge, meaning that the carbonizedfiber skeleton is preferably not pulverized into a fine powder beforesintering. The nano-metallic sponge forms on and around the carbonizedfiber skeleton, leading to a hollow tube structure with a very highsurface area-to-volume ratio during the late sintering process.Nano-metallic sponges may be formed in a single, continuous process,comprising heating the fiber to form nanoparticles embedded in thecarbonized fiber skeleton, and then raising the temperature untilnano-metallic sponges are formed. In another alternative, thenano-metallic sponges (or the core-shell nanoparticles, for that matter)may be formed in situ with the ion-impregnated fibers. Or thenano-metallic sponges may be formed in two steps: First, thenanoparticles are formed, embedded in the carbonized fiber skeleton, inone location. Second, the carbonized skeleton with nanoparticles ispositioned in a designated place and heated to form a sponge with afresh surface in situ, in a second location, where the sponge is to beused (typically, as a catalyst). This last approach may be particularlyattractive for industrial applications. Because metal catalysts canoften be sensitive to ambient conditions, it can be useful to prepare acatalyst with a fresh surface directly inside a reactor only whenneeded.

At this higher temperature metal nanoparticles sintered andinterconnected, forming nano-sponge structures. The fiber skeletonprovided a frame/template to generate tube-like nano-sponges as shown inFIGS. 7A-7C and FIGS. 8A-8B. FIGS. 7A-7C depict Cu/C nano-metallicsponges, and FIGS. 8A-8B depict Ag/C nano-metallic sponges. Thenano-metallic sponges exhibited large surface areas. The resultingnanoparticle structures may be used either without support or withanother support structure. Further nano-metallic sponges may comprise amixture of one or more metals. Nano-metallic sponges made in accordancewith the present invention are expected to exhibit a high number ofactive catalytic sites per unit volume.

Uses for the Novel Materials

Copper nanoparticles, for example, have many industrial applications dueto their unique physical, optical, and chemical properties, but they aregenerally extremely sensitive to their environment. Coating coppernanoparticles with a carbon layer appears to protect the copper againstoxidation, while allowing the particles to retain useful properties.Other encapsulated metals, such as Ni, Zn, Fe, Cr, Pt, Pd, W, Re, andmixtures of metals, may be used in applications, such as catalysis andprotection of wood and live plants. In addition, the carbon shells alsoprovide surfaces for chemical functionalization or surface modification.Surface modifications may be used in applications such as biological andbiomedical diagnoses, catalysis, fuel cells, drug delivery, paint andcoating technology, sonar, and magnetic particle technology.

Wood Preservative

Copper-based reagents are known to be effective wood preservatives, butas noted above, current formulations tend to leach from wood in thepresence of moisture, they tend to corrode metal fasteners, and they maycause wooden structures to emit offending vapors. While low oxidationstate copper nanoparticles otherwise rapidly oxidize in air, by coatingthe surface of copper nanoparticles with a thin carbon layer we wereable to protect Cu⁰ against oxidation. However, even though the copperwas coated, it retained its wood preservation properties. Our novel formof copper, CCCSNPs, was effective for wood preservation, protecting forexample against Formosan termites and decay, while it persisted in woodin the presence of moisture. This novel material did not cause corrosionof metal hardware, nor did it give off offensive vapors. CCCSNPsappeared to be environmentally friendly wood preservatives, since copperions were not readily leached, nor readily discharged into theenvironment.

The novel nanoparticles may be used in various wooden structures,including lumber, structural wood composites or lumber composites,laminated veneer lumber, parallel strand lumber, laminated strandlumber, non-structural wood composites, particleboard, hardboard, mediumdensity fiberboard, and wood fiber-cement composites. CCCSNPs also maybe incorporated into a composite either while being made or after beingformed, and they may be inserted into wood using standard pressurizationtechniques, or they may be taken up directly by living plants.

Catalysis

Cellulose is a natural carbohydrate (polysaccharide) containinganhydroglucose units joined by an ether linkage to form a linearmolecular chain. Natural cellulose fibers have a porous structure, withinterconnecting microfibrils 10-30 nm in width. Specific surface areasare usually in the range of 30-55 m²/g. FIGS. 3A and 3B are micrographsof cellulose. FIG. 3A depicts the surface of cellulose; and FIG. 3Bdepicts the pores. Wood has complex pore morphology within its cellulosefibers. We have used this morphology for synthesizing nanoparticles,enhancing the access of reactant molecules to catalytic centers.

In one embodiment, catalysts may be made from nano-metallic sponges.Nano-metallic sponge structures, made in accordance with the presentinvention without exposure to air, were nearly completely active metal.Upon exposure to air, metal oxides were formed. When a metallic-spongeis made from catalytically active metals it should either be reduced insitu or kept under a non-oxidizing atmosphere before use as a catalyst.Mixtures of metals in nano-metallic sponges may also be made.

Strengthening Polymer and Polymer Composite Materials

MCCSNPs may be used to strengthen polymeric systems, including, forexample polyethylene terephthalate (PET), high density polyethylene(HDPE), polyvinyl chloride (PVC), low density polyethylene (LDPE),polypropylene (PP), polystyrene (PS), other polymers (e.g., SAN, ABS,PC, and nylon), their combinations (e.g., PET/HDPE systems), and fiberreinforced composites from various polymers.

CCCSNPs were used as impact modifier/coupling agent for HDPE andHDPE-natural fiber composites through a melt-blending process. Theresults showed improved impact strength. It is expected that othermetal-core carbon-shell nanoparticles will also be useful for thispurpose.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A depicts an SEM image of a carbonized cotton fiber impregnatedwith Cu.

FIG. 1B depicts a TEM image of Cu nanoparticles in the carbonized cottonfiber.

FIG. 1C depicts a TEM image of a single Cu-core Carbon-shellnanoparticle.

FIG. 1D depicts a nanoparticle as depicted in FIG. 1C at highermagnification.

FIG. 1E depicts an electron diffraction pattern of a Cu-corecarbon-shell nanoparticle.

FIG. 1F depicts a higher magnification of a carbonized cotton fiberimpregnated with Cu.

FIG. 2A depicts a TEM image of Cu nanoparticles in carbonized rayon.

FIG. 2B depicts a TEM image of Cu nanoparticles as depicted in FIG. 2Ain carbonized rayon at higher magnification.

FIG. 2C depicts a TEM image of Cu nanoparticles as depicted in FIG. 2Bin carbonized rayon at higher magnification.

FIG. 3A depicts a micrograph of the surface of cellulose.

FIG. 3B depicts a micrograph of the pores in cellulose.

FIG. 4A depicts a TEM image of Ag nanoparticles in carbonized cottonfiber.

FIG. 4B depicts a TEM image of Ag nanoparticles in carbonized cottonfiber at higher magnification.

FIG. 5A depicts the amount of Cu-core carbon-shell nanoparticles takeninto pine branches immersed in a slurry of Cu nanoparticles.

FIG. 5B depicts the amount of Cu-core carbon-shell nanoparticles takeninto pine branches immersed in a slurry of Cu nanoparticles.

FIG. 6 depicts a TEM image of Gd nanoparticles in carbonized cottonfiber.

FIG. 7A depicts an SEM image of a Cu-Sponge.

FIG. 7B depicts an SEM image of a Cu-Sponge at higher magnification.

FIG. 7C depicts an SEM image of a Cu Sponge at higher magnification.

FIG. 8A depicts an SEM image of a Ag-Sponge.

FIG. 8B depicts an SEM image of a Ag-Sponge at higher magnification.

FIG. 9 depicts a graph of concentration of Cu in leachate vs. leachingtime for leaching of Cu-core carbon-shell nanoparticles from wood.

FIG. 10 depicts weight loss of wood due to termites as a function oftreatment.

FIG. 11 depicts mortality of termites as a function of treatment.

FIG. 12A depicts the loading of copper in samples tested for decay andleaching.

FIG. 12B depicts the loading of copper in samples tested for termites.

FIG. 13 depicts weight loss of wood due to T. versicolor (decay) as afunction of treatment.

FIG. 14 depicts weight loss of wood due to Irpex lacteus (decay) as afunction of treatment.

MODES FOR CARRYING OUT THE INVENTION

The general method for producing novel metal-core carbon-shellnanoparticles comprises soaking a natural fibrous material with asolution containing metal ions, removing the solvent, and thencarbonizing the impregnated fibers at a temperature sufficient togenerate metallic cores encased in carbon shells.

In a prototype example, we used cotton fiber as template, which wassoaked in a copper sulfate solution and then extra solvent was removed.Next, we carbonized the copper-impregnated cotton fiber by heating it tobetween about 200° C. and about 400° C., with a preferred temperature ofabout 350° C. Carbonization may be carried out between a few seconds andabout 3 hours, with a preferred carbonization time of about 2 hours.Carbonization may be carried out in an inert atmosphere, for exampleunder nitrogen, or in vacuum. Carbonization may also be conducted inother non-oxidizing gases such as He, Ne, Ar, Kr, or Xe. In addition,carbonization may be carried out in reducing atmospheres, for exampleH₂, CH₄, etc. While not preferred, carbonization also may be carried outin an atmosphere that contains limited amounts of oxygens or otheroxidizing agents, if the amounts do not adversely affect the results.While not wishing to be bound by this theory, it appears thatcarbonization can transform oxygen into CO, which is reducing, or intoCO₂, which is non-oxidizing. The preferred atmosphere for carbonizationis under nitrogen. The time and temperature for carbonization depend onmetal ions and fibers used.

Copper-core carbon-shell nanoparticles (“CCCSNs”) were formed during thecarbonization processes without requiring further treatment. CCCSNPsappeared to be uniformly distributed throughout the carbon matrixgenerated during the carbonization. FIGS. 1A, 1B, 1C, 1D and 1F depictelectron micrographs of fabricated copper-core carbon-shellnanoparticles made through the present invention. FIG. 1E depicts anx-ray diffraction pattern of a copper-core carbon-shell nanoparticle.FIG. 1A depicts an SEM image that shows the carbonized cotton fiber(carbon black) with many nanoparticles on its surface; FIG. 1B depicts aTEM image demonstrating that the nanoparticles were distributedthroughout the carbonized cotton fiber. FIG. 1C depicts a copper corewith a carbon shell surrounding it. As can be seen from FIGS. 1C and 1D,the copper core appeared to be about 50-60 nm in diameter, and thecarbon shell appeared to be about 5 nm thick, respectively. FIG. 1Cdepicts a nanoparticle as depicted in FIG. 1D at lower magnification.FIG. 1E depicts electron diffraction pattern of Cu-core carbon-shellnanoparticle as depicted in FIG. 1C. This electron diffraction patternindicated that the copper is in a Cu⁰ metallic state. FIG. 1F depicts ahigher magnification of carbonized cotton fiber as depicted in FIG. 1B.

This invention may be carried out using almost any metal that formssoluble ions in either aqueous or non-aqueous solvents, except thatgroup IA metals (Li, Na, K, Rb, and Cs) may be too electropositive.Silver-core carbon-shell nanoparticles, nickel-core carbon-shellnanoparticles, and gadolinium-core carbon-shell nanoparticles have allbeen successfully made. FIGS. 4A and 4B show electron micrographs ofAg-core carbon-shell nanoparticles at different magnifications. FIG. 6shows an SEM micrograph of the Gd core/shell prototype.

Nickel-core carbon-shell nanoparticles were generated using the samemethod as described above for copper, using NiSO₄ as the source of Ni,except the carbonization temperature was 380° C.

Silver-core carbon-shell nanoparticles were generated using the samemethod as described above for copper, except silver nitrate was used asthe source of silver, and the carbonization temperature was 180° C.

Galladium-core carbon-shell nanoparticles were made using the samemethod as described for the Cu version except GdCl₃ was used as the Gdsource, and the carbonization temperature was 350° C.

While not wishing to be bound by this theory, it appears that thecarbonization temperature correlated roughly with the melting point ofthe metal.

Cu-core carbon-shell materials have been successfully used to protectwood against decay.

Gd-core carbon-shell materials may be used, for example, in NMR imageenhancement, energy-efficient magnetic refrigeration, and data storage.Other lanthanum-group metals, including Ce, Pr, Nd, Pm, Sm, Eu, Tb, Dy,Ho, Er, Tm, Yb, and Lu also may be used to form MCCSN materials, andthese materials also should be useful for similar purposes.

Alternatively, the present invention may be used to makethree-dimensional nano-metallic sponges. The process is generallysimilar to that for making the core/carbon shell nanoparticles, but themetal ion-impregnated natural fibers are heated to a higher temperature,to a point where carbon is vaporized, and the metal nanoparticles juststart to sinter and connect to one another to form nano-spongestructures. The fiber skeleton acts as a frame/template to maketube-like nano-sponges, which have a far greater surface area/volumeratio than most prior nanoparticle structures. We have madethree-dimensional nano-metallic structures, which exhibited high surfacearea, and which typically had particle sizes less than 10 μm, andpreferably less than 50 nm, and more preferably less than 10 nm, asestimated from SEM micrographs. The metal typically existed in a lowoxidation state, and in a preferred embodiment, the metal was in a zerooxidation state. Pore sizes of the metallic sponges were typically lessthan 100 μm, and preferably less than 100 nm, and more preferably lessthan 10 nm, as estimated from SEM micrographs. The sponges may existwithout a carbon coating. The sponges may comprise a mixture of metals.

Prototype nano-metallic sponges have been made by soaking natural fibersin a metal ion solution as previously described, followed by carbonizingthe impregnated fibers at elevated temperature in an inert atmosphere(or under vacuum). A somewhat higher temperature is used to formnano-metallic sponges than the core/shell nanoparticles. We have foundthat for copper a preferred temperature for forming core/shellnanoparticles is about 350° C., and a preferred temperature for formingnano-metallic sponges is about 450° C. For silver, the correspondingtemperatures are about 180° C. and about 280° C., respectively.

FIGS. 7A, 7B, and 7C depict electron micrographs of Cu/C nano-metallicsponges at different magnifications; FIGS. 8A and 8B depict electronmicrographs of Ag/C nano-metallic sponges at different magnifications.In both cases, note the tubular shapes, the high porosity walls, and thehigh surface areas. Nano-metallic sponges may be used in catalysis.

Example 1

The surface of the cellulose fiber is rough (FIG. 3A) and contains poresof diameter of 30-70 nm (FIG. 3B). These nanopores may allow reactantmolecules to penetrate into inner cavities. When cellulose fibers wereimmersed in aqueous CuSO₄, copper ions were readily impregnated into thecellulose fibers through the pores. Though not wishing to be bound bythis theory, most of the incorporated Cu⁺⁺ ions appeared to be bound tocellulose macromolecules, probably via electrostatic (e.g., ion-dipole)interactions, with the electron-rich oxygen atoms of polar hydroxyl andether groups of cellulose.

Example 2

Cotton fiber was soaked in a copper sulfate solution. After the cottonwas saturated, then extra solvent was removed. Carbonization was carriedout at about 350° C. under nitrogen for about two hours. The coppernanoparticles and the encapsulating carbon shells appeared to have beenformed simultaneously during carbonization. As fabricated, the CCCSNPswere uniformly distributed throughout the carbon based matrixes. FIGS.1A, 1B, 1C, 1D, and 1F depict micrographs of fabricated copper-carboncore-shell nanoparticles made through the present invention. FIG. 1Adepicts an SEM image that shows the carbonized cotton fiber (carbonblack) with many nanoparticles located on its surface; FIG. 1F depicts ahigher magnification of that depicted in FIG. 1A. FIG. 1B depicts a TEMimage demonstrating that the nanoparticles formed through the entirecarbonized cotton fiber; FIGS. 1C and 1D depict TEM micrographs of ananoparticle encased in a carbon shell. These micrographs show a core ofabout 50-60 nm in diameter and a carbon shell of about 5 nm. FIG. 1Edepicts an x-ray diffraction pattern for nanoparticle depicted in FIGS.1C and 1D. This pattern confirms that the copper remained as Cu⁰.

Example 3

The total copper concentration in the material made according to Example2 was measured to be about 25 Wt %. It was clear from the TEM micrograph(See FIG. 1B) that the particles had generally spherical shapes, andthat a majority of them appeared to have an average diameter value about20-50 nm, although some particles were as small as one or two nanometersin diameter.

After the carbonized material was pulverized into micrometer tosub-micrometer sized particles, it was uniformly dispersed into bothpolar and non-polar solvent, for example water, aqueous acids, aqueousbases, salt solutions and cooking oil. After being immersed in water atambient environment over three months, the nanoparticles still retaineda reduced copper core structure with no sign of deterioration. Thepowder, characterized by FTIR, also showed that the shells of the CCCSNparticles retained a number of organic functional groups. This propertywill be useful in functionalizing the carbon layer.

Example 4

Cotton fiber was soaked in a AgNO₃ solution. After the cotton wassaturated, then extra solvent was removed. Carbonization was carried outat about 180° C. in nitrogen for about two hours. FIGS. 4A and 4B depictelectron micrographs of the carbon-encased silver nanoparticles, atdifferent magnifications.

Example 5

Cotton fiber was soaked in a NiSO₄ solution. After the cotton wassaturated, then extra solvent was removed. Carbonization was carried outat about 380° C. in nitrogen for about two hours. The resultingnanoparticles contained carbon encased Ni, but the nanoparticles weredifficult to distinguish with electron microscopy.

Example 6

Cotton fiber was soaked in a GdCl₃ solution. After the cotton wassaturated, then extra solvent was removed. Carbonization was carried outat about 350° C. in nitrogen for about two hours. FIG. 6 depicts amicrograph of Gadolinium encased nanoparticles.

Example 7

The processes described in Examples 2, 4, and 6 were repeated usingrayon fibers, wood fibers and cotton paper. All other reagents andconditions were the same. FIGS. 2A, 2B and 2C depict a micrograph of Cuin rayon.

Example 8

The process described in Examples 2, 4, and 6 have been used to makenanoparticles from a solution containing multiple metals, for example Cuand Ag. It appears that a Cu—Ag mixture was formed.

Using Copper Based Preservatives for Wood Protection Example 9

The novel nanoparticles may be introduced into wood in the same generalmanner as other wood preservatives, e.g., pressure treatment. It isbelieved that this is the first report of using carbon-coated coppernanoparticles in the treatment of wood to protect against insects, mold,or decay.

There are several advantages to using CCCSNPs as wood preservatives. Thecellulose source may be derived from bio-based renewable raw materials.Smaller amounts of Cu ions will be released in the environment due tothe carbon encapsulation and lower metal loading. The material may bemade at a competitive cost. The product is dispersible in both water andoil. The novel form of copper is compatible with existing wood treatingprocesses in industry.

Example 10

Copper is toxic to marine life, particularly in the +1 or +2 oxidationstate. One of the advantages of CCCSNP powder is that the encased copperwill remain as metallic copper. We tested the stability of the CCCSNP byimmersing the particles in a variety of solvents as listed in Table 1.

TABLE 1 Experimental design for chemical stability tests in designatedsolvents No. of Solvent Condition Tests 1. water (pH = 7) and 1, 5, 10,20, 30, 40, 50, 60, 90 days 36 (pH = 2) (t = 25° C. & 40° C.) 2. 3% wtNaCl (pH = 7) 1, 5, 10, 20, 30, 40, 50, 60, 90 days 36 and (pH = 2) (t =25° C. & 40° C.) 3. Hexane 1, 5, 10, 20, 30, 40, 50, 60, 90 days 18 (t =25° C. & 40° C.) Total Number of tests 90

For all conditions tested (Table 1), we found that the copper remainedstable as metallic copper, Cu⁰.

Example 11

A suspension of 1% CCCSNP in water was used to treat wood samples usinga standard vacuum and pressure treatment, otherwise similar to thatcommonly used in wood treatment plants. The treated samples weresubsequently challenged with Formosan subterranean termites (Coptotermesformosanus Shiraki) using the AWPA El-jar test standard. The resultsshowed that the novel materials greatly inhibited termite attacks on thetreated samples.

Example 12

CCCSNP was combined with other biocides to form various preservativesystems to deal with both copper-resistant and non-copper resistantfungi. Such co-biocides may include, for example, quat, tebuconazole(C₁₆H₂₂ClN₃O), RH287, and others known in the art. Tebuconazole andRH287 were formulated into emulsions to mix with the CCCSNP.

Example 13

Commercial #2 grade 2″×4″ lumber from southern pine (Pinus spp.) andwestern spruce (Pica spp.) were cut into 48-inch long samples. The endsof each sample were coated with a commercial lumber sealer such asANCHORSEAL® by U.C Coatings Corporation a “lumber end paint type” byCloverdale Paint. The samples were pressure-treated based as shown belowin Table 2.

TABLE 2 Experimental design on pressure-treatments with CCCSN solutionVariable Condition Treatments 1. Wood Species Southern Pine and Western2 2. Treatment Pressure (PSI) Spruce 120 and 160 2 3. CCCSN-Basedsystems Quat, Azole, and RH287 3 4. Concentration (wt %) 0 (control), 1,2, and 5% 4 5. Treating Process 30-minute vacuum at 30-inch 1 Hg and60-minute pressurizing at target pressure level Total Number ofTreatments 48

A Twin-X x-ray preservative analyzer (Model 54-C-TX01—Oxford InstrumentsAnalytical Ltd.) was used to analyze copper loading in CCCSNP powder andin treated lumber. For treated lumber, small thin wood slices, takenfrom various depths for each treated panel, were examined. The sampleswere ground into powder (40-mesh) and analyzed for copper. CCCSNP powderdistribution and the copper penetration profile as the function oftreatment conditions and wood morphology were determined by environmentscanning electron microscopy (ESEM) with X-ray microanalysis.Micro-distribution of copper was also determined using scanning electronmicroscopy (SEM) with X-ray microanalysis. X-ray surface mapping andline scan provided the distribution surface elements as well asmorphology information. X-ray image-chemical analyzer (EDAX) analysisshowed copper within the wood; however, detail analysis will requirehigher Cu loadings in the wood. Micro-distribution of the copper withinthe wood, especially along the board thickness will be determined in thefuture.

Example 14

Leaching Tests.

Water leaching experiments were conducted according to AWPA leachingstandard E11-97 [AWPA 2001c]. CCCSNP treated wood samples (19.0-mmcubes) were compared to Alkaline Copper Quaternary (“ACQ”)-treatedsamples. The samples were subjected to AWPA leaching procedures over atotal 14 day period. Leachate was removed at designated intervals. Thetotal copper content in the leachate was analyzed as a function of timeby Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES).The method has a detection limit of about 0.1 mg/1, which is generallyreproducible within ±8% for all analytes. The percent of copper leachedis shown in Table 3 below and in FIG. 9. Group B, D, E, and H aredescribed in Table 4. As can be seen the CCCSNPs were retained in thewood substantially better than the standard copper formulation, ACQ.

TABLE 3 Copper concentration in the leachate as a function of leachingtime measured ICP technique. Copper Concentration (ppm) Control, TimeUntreated (Hours) ACQ Wood B group D-group E-group H-group 6 23.28 0.01617.51 6.37 22.00 23.72 30 27.34 0.005 7.02 3.06 14.94 13.79 78 18.910.011 1.52 0.92 3.99 3.42 126 11.23 0.006 0.79 0.45 2.28 0.79 174 9.770.003 0.59 0.37 0.48 0.27 222 7.38 0.003 0.27 0.22 0.19 0.14 270 4.220.01 0.31 0.19 0.16 0.42 318 5.67 0.00 0.24 0.12 0.11 0.04 366 6.31 0.010.22 0.11 0.10 0.06

Example 15

Termite Resistance Tests.

Five matched samples for each treatment condition, five ACQ treatedsamples and five untreated southern pine controls, were used inNo-Choice Laboratory Termite Tests according to a modified AWPA standardE1-97 [AWPA 2001a]. FIG. 12B depicts the loadings of copper for thetermite tests. Prior to each test, the blocks were oven-dried at 105° C.for 24 hours, and sample weight (W₁) and dimensions were measured. Eachtest bottle (80 mm diameter×100 mm height) was autoclaved for 30 minutesat 105 kPa and dried. Autoclaved sand (150 g) and distilled water (30mL) were added to each bottle. Finally, four hundred termites (360workers and 40 soldiers) were added to opposite sides of the test blockin the container. All containers were maintained at room temperature for4 weeks. The bottle cap was placed loosely. After testing, each bottlewas dismantled. Live termites were counted, and test blocks were removedand cleaned. Each block was oven-dried again at 105° C. for 24 hours todetermine the dry sample weight (W₂). From the measurements, sampleweight loss [(W₁−W₂)/W₁] and termite mortalities were determined. Thetested samples were ranked visually by five people on a scale of 1-10,with 10 as no damage and 1 as complete destruction. Table 4 below showsthe results of this test. In the table both percent mortality and weightloss are given as well as a statistical ranking based on the Ducanprotocol. Groups with different letters, for example A or B, indicatethat the value in the table associated with one letter is statisticallydifferent from the value in the table associated with another letter. Agroup with two letters, for example CD, indicates the value in the tablecannot be distinguished from either of the groups with those letters.For example CD could not be distinguished from a group designated C orfrom a group designated D. By both weight loss and termite mortality itwas clear that CCCSNP is effective against termites. FIG. 10 depicts theloss of wood as a function of treatment. FIG. 11 depicts termitemortality as a function of treatment.

TABLE 4 Summary of Termite Test Results Copper loading Sample Damagerate Mortality Weight Rating Group (kg/m³) Rate (%) Loss (%) (0-10)Group A 0.50 32.50% BC  8.75% B 6.5 B Group B 0.74 42.30% C  2.80% A 8.3CD Group C 0.41 38.40% BC  2.25% A 8.4 CD Group D 0.51 34.90% BC  1.90%A 8.8 D Group E 0.62 22.20% AB 11.33% B 6.4 B Group F 0.73 25.85% BC 3.35% A 8.3 CD Group G 0.48 30.05% BC  4.07% A 7.8 C Group H 0.6533.71% BC  4.33% A 8.1 CD ACQ Control 3.67 21.89% AB  2.05% A 9.9 E WoodControl 0.01  9.04% A 32.09% C 1.0 A

Note that at a Cu loading for the ACQ control was about five to ninetimes the Cu loading for the Cu-core carbon-shell nanoparticles, whilethe effectiveness for termite control was about the same or better forthe CCCSNP-impregnated wood at a far lower loading of copper.

Example 16

Flake Preparation.

Commercial dry southern pine and mixed hardwood flakes were obtained.Part of the flakes were sprayed with a CCCSNP-based mixture (alsoincluding quat, tebuconazole, and RH287, based on solid wood tests) toachieve target copper loading levels around 0.25 and 0.45 wt %. Themixed flakes were used for making a composite wood product withincorporated CCCSNP.

Panel Manufacture.

Experimental panels were manufactured using treated and control flakesaccording to the following conditions:

TABLE 5 Experimental design for strand board manufacturing withCCCSN-treated flakes. Variable Condition Treatments 1. Wood SpeciesSouthern Pine and mixed 2 hardwoods 2. Panel Density (g/cm³) 0.70 1 3.Copper loading 0.25 wt %, 0.45 wt % 2 4. Resin Content (%) 4.5% of drywood weight 1 5. Panel Size 24 × 24 × 0.5-inch 1 6. Panel StructureSingle-layer random-formed 1 7. Replication Three each 3 Total Number ofTreatments 12

The flakes and panels described above will be made. For each condition,the target amount of wood, resin, CCCSNP, and wax (used as a binder)will be weighed and mixed in a blender. Liquid resin and wax will beforced through two separate air-assisted nozzles, causing fine dropletsto be sprayed into the blender with wood flakes. The CCCSNP powder willbe added by a third air-assisted nozzle at about 40 PSI pressure. Theseconditions are similar to those used in a conventional process forloading zinc borate into wood. The blended wood flakes will then beremoved and formed into mats. The mats will be hot-pressed into panels(1 minute closing and 5 minutes curing) using a 200-ton hot press. It isexpected that such panels will be resistance to termites, mold anddecay.

Example 17

As shown in Table 6, selected weights of CCCSNP were mixed with 1000 mlof water. Wood samples were placed in a 2000 ml plastic container, whichwere evacuated to about 27 mm-Hg for 30 minutes. The treating slurrieswere then introduced into the containers. The assembly, comprising woodand treating slurry, was then pressurized to 130 PSI (0.9 MPa) for about60 minutes. After pressure was released, samples were removed, and thendried at about 80° C. to a constant weight. The treated samples werestored in plastic bags for subsequent testing.

TABLE 6 Formulation of the treating solution with 1000 ml water. Amountof Amount of Amount of Group CCCSNP Quaternary EDTA Group A 10 g 0 g 0 gGroup B 20 g 0 g 0 g Group C 10 g 6 g 0 g Group D 20 g 6 g 0 g Group E20 g 0 g 15 g  Group F 20 g 6 g 15 g  Group G 10 g 6 g 0 g Group HMixture of Groups A-G

Example 18

CCCSNP-treated wood samples (19 mm cubes) prepared as described inExample 17 were tested for resistance to decay/leaching. These resultswere compared with commercial ACQ-treated wood samples of the same size.Three random samples were selected from each group. Samples werehammer-milled to 20-mesh. The powder was then digested in a sulfuricacid (42.5 ml)-water (200 ml) solution for three days. The digestedsolution was then filtered and diluted to 500 ml with water and analyzedfor Cu content by Inductively Coupled Plasma Atomic EmissionSpectrometry (ICP-AES). The copper concentration (kg/m³) was calculatedfor each group based on measured sample volume and total copper content.FIG. 12A depicts the loading of copper for several of the samples.

Example 19

The decay resistance of CCCSNP-treated wood samples was tested accordingto AWPA standard E10-01 [AWPA 2001b]. White fungi, Trametes versicoloror Irpex lacteus, were used in the test. The culture media weresterilized at 105 kPa for 30 minutes at 105° C. and cooled beforeinoculation. 100 g of silt loam screened through a No. 6 sieve wereplaced in each bottle, which was loosely capped and autoclaved twice at105 kPa for 30 minutes at 105° C. After the bottles cooled, untreatedsouthern pine wood feeder strips were placed on top of the soil in eachbottle. Each feeder strip was then inoculated at diagonally oppositecorners. Each inoculated bottle was be incubated at 25° C. and 75%humidity until the feeder strip was heavily colonized by test fungus.The test blocks were then placed on the surface of a feeder stripcolonized with fungus, one in each bottle. The testing time for bothwhite rot fungi was 16 weeks. After the test, the test blocks wereremoved, cleaned, and oven-dried. Sample weight loss was calculated andanalyzed. FIGS. 13 and 14 show the results of these tests. FIG. 13depicts weight loss due to decay from Trametes versicolor. FIG. 14depicts weight loss from decay due to Irpex lacteus. Clearly the CCCSNPsare effective against these decays. Further, as can be seen from FIG.12A, the copper loading for the AQC standard sample is 5-10 times thatof the CCCSNPs. Thus, on a per weight basis the CCCSNPs are moreeffective than the commercial standard.

Example 20

Wood/Natural Fiber-Polymer Composites (WNFPC)

Melt-blending and compression molding methods were used to manufacturethe Wood/Natural Fiber-Polymer Composites (WNFPC) with CCCSNP additive.During melt-blending, high density poly-ethylene (“HDPE”) pellets wereloaded into a Haake Rheomix 600 blender set at 165° C. and 60 RPMblender speed. After HDPE melting, CCCSNPs were added to the melt. Inone embodiment wood fiber (40-mesh particle size) was added to the mix.In another embodiment bagasse fiber was added to the mix. A mixingperiod of 10 minutes was used to mix all components completely (i.e.,the mixing torque reached stable conditions). The blend was cooled andremoved from the blender.

The blends with various compositions were then used to make impact andtensile/dynamic mechanical analysis (DMA) test panels (4- and 1-mmthick, respectively) using compression molding. For each sample, themolding set was pressed at 175° C. and 30-ton compression force for 5minutes, and then cooled to room temperature while maintaining thepressure. The target density was 1.0 g/cm³. The test panels wereconditioned prior to cutting of test samples. Test samples were machinedand tested for tensile strength, impact strength, and dynamic modulus.See Table 7. These data show the ease with which the CCCSNPs may beincluded during fabrication of composites. Further, the compositescontaining CCCSNPs showed improved impact strength and tensile strengthas compared to control composites, while dynamic modulus appears to beabout the same as the control for most formulations tested. Thesecomposites are expected to be resistant against termites and decay justas impregnated wood was.

TABLE 7 Summary of test data on wood/natural fiber polymer compositesComposition Dynamic Tensile Formulation Wood Bagasse Modulus StrengthImpact Strength Number HDPE Fiber Fiber CCCSNP (MPa) (MPa) (KJ/m²) 01 100%  0%  0%   0% 1543 27.37 3.96 02 98.5%  0%  0% 1.5% 1545 29.31 4.5703 70.0%  0% 30%   0% 2348 23.22 3.74 04 68.5%  0% 30% 1.5% 2875 30.374.98 05 70.0% 30%  0%   0% 2474 19.97 3.02 06 68.5% 30%  0% 1.5% 218320.35 3.37

Example 21 Application to Trees

Four freshly cut pine branches, about 0.5 inches in diameter, wereplaced in glass tubes with one branch per tube. The tubes containedCCCSNP slurries at weight percentages of 0.0%, 0.5%, 1%, and 2%. Thebranches were kept in these tubes for about 10 days, after which theywere removed and sacrificed. The wood was examined with ICP. FIG. 5Adepict the concentration of Cu in the tree branch as a function ofdistance from the bottom of the branch. Data from the branch inserted inthe 2% slurry showed a concentration of about 25 ppm Cu at about 2inches from the bottom. The Cu concentration decreased as a function ofdistance from the base, and was detected at about 5 ppm at about 12inches from the base.

Example 22

Two rose bushes were planted in standard nursery soil. One was wateredwith 1.5% slurry of CCCNSP, and the other bush was watered with purewater. After about three weeks we sacrificed the plants and determinedthe copper content as a function of distance from the trunk bottom usingICP. The first approximate 2 inch of the plant was in the soil. FIG. 5Bdepicts the concentration of Cu in the rose bush stem as a function ofdistance from the bottom of the plant. A peak in Cu concentrationoccurred at about 6″ from the tree bottom. The concentration of Cu atits maximum was about 4.3 ppm.

Example 23

Different fibers (cotton, wood, bagasse, etc.) will be used to generatecore-shell nanoparticles. As-harvested fibers will be compared topre-treated (de-greased) fibers in terms of the resulting core-shellstructure, particle size distribution, and particle density within thefiber, to determine whether the benefits of de-greasing justify thecosts for use in the novel process.

Example 24

For some uses it will be useful to separate and collect the core-shellnanoparticles from the carbon matrix. For other uses, such as woodpreservation, separation may not be necessary. In wood preservation,retaining the carbon matrix may actually be beneficial, both to betterabsorb other compounds that may also be helpful in wood protection, andalso to help disperse the nanoparticles more uniformly through the woodstructure. The “carbon matrix” comprises the black carbon residuecompounds from the carbonized fibers. The “carbon shell” comprises thecarbon layer(s) that are closely bonded to a metal nanoparticle core,typically with a thickness of a few nanometers. We have seen in TEMobservations that the carbon shell on the copper nanoparticle surfacehas a different microstructure from carbon in the matrix. The FTIRresults showed that there were substantial quantities of carbohydratemolecules in the carbon matrix but not in the shells. These differencesmay be exploited to separate core/shell nanoparticles from the matrix bychemical means, physical means, or both.

Separation methods include: (1) pulverizing the carbonized fibers withembedded nanoparticles to a fine powder, and screening the resultingpowder from 100 μm to sub-μm to determine an optimal screen size forseparation; in general, it is expected that finer powders and finerscreens will yield better results, but may take more effort; (2) mixingthe powder with an organic solvent such as acetone, so that thecore/carbon shell nanoparticles start to separate from the carbonmatrix, with stirring if needed. Preferably, the density and viscosityof the solvent are such that the carbon matrix with remain suspended,while the metal core nanoparticles will settle; (3) using ultrasonic,magnetic, centrifuge, or mechanical stirring will increase theseparation speed and reduce the time needed for separation. Becauseacoustically cavitated bubbles produce high pressures, high pressuregradients, and fluid motion, this technique also may accelerate theseparation processes; (4) separation may also be accomplished byapplying a vacuum over a suspension containing a mixture ofnanoparticles and carbon. Nanoparticles are expected to be pulled intothe vacuum and collected directly with an air filter system. The carbonmatrix phase will be examined by Energy Dispersive Spectroscopy (EDS)X-Ray Microanalysis and TEM to determine quantitative separation ratiosand size effects on separation, respectively.

Example 25

Mold Tests.

Mold testing will also be conducted following the testing procedures inAWPA “Standard Method of Evaluating the Resistance of Wood ProductSurfaces to Mold Growth.” Molds and their spores will include:Aureobasidium pullulans (d. By.) Arnaud ATCC 9348; Aspergillus niger v.Tiegh. ATCC 6275; Penicillium citrinum Thom ATCC 9849; and Alternariatenuissima group (Kunze) Wiltshire Ftk 691B. The collected inocula willbe dispersed in distilled water and distributed on potting soil in themold chambers. The mold chambers will be left in warm humid conditionsfor more than two weeks prior to placing in the samples. Thetemperatures and humidity of the room will be periodically checked. Themold chamber will be kept at 25° C. and 100% humidity. Samples will berated every 2 weeks for a total of 5 rating periods following the ratingsystem in the AWPA proposed standard.

DEFINITION

As used in the specification and claims, unless context clearlyindicates otherwise, a “biological fiber” means a native plant fiber, anative animal fiber, a chemically- or physically-modified plant fiber,or a chemically- or physically-modified animal fiber. If the nativefiber is chemically or physically modified, then its structure shouldretain sites that are effective as centers for promoting the formationof metallic core-carbon shell nanoparticles. The term “biological fiber”does not include synthetic fibers, regardless of composition or chemicalor structural similarity, that are not derived from native plant fibersor native animal fibers. Examples of fibers that are not considered“biological fibers” include the various synthetic nylons and polyesters.

The complete disclosures of all references cited in this specificationare hereby incorporated by reference. In the event of an otherwiseirreconcilable conflict, however, the present specification shallcontrol.

What is claimed:
 1. Metallic nanosponges formed by a method comprisingthe steps of: (a) impregnating biological fibers with a solution ofmetal ions in an aqueous or non-aqueous solvent; (b) removing solvent,while leaving at least some of the metal ions impregnated in the fibers;and (c) heating the metal-ion-impregnated fibers in a non-oxidizingatmosphere or in a vacuum to a temperature or temperatures thatinitially carbonize at least some of the fibers, that then reduce atleast some of the metal ions to metal particles in a zero oxidationstate, and that then vaporize the carbon to produce metallic, highlyporous nanosponges comprising zero-oxidation-state metal.
 2. Themetallic nanosponges of claim 1, wherein the biological fibers areselected from the group consisting of cellulose, hemi-cellulose, lignin,cotton, rayon, flax, linen, jute, ramie, sisal, hemp, milkweed, straw,bagasse, hardwood, softwood, lepidopteran silk, hair, wool, spider silk,sinew, and catgut.
 3. The metallic nanosponges of claim 1, wherein themetal ions are selected from ions of the group consisting of Group HAmetals (Be, Mg, Ca, Sr, Ba, Ra); Group IIIA metals or semi-metals (B,Al, Ga, In, Tl); Group IVA metals or semimetals (Si, Ge, Sn, Pb); GroupVA metals or semi-metals (As, Sb, Bi); Group VIA semi-metals (Te, Po);Group IIIB metals (Sc, Y, La, Ac); Group IVB metals (Ti, Zr, Hf): GroupVB metals (V, Nb, Ta); Group VIB metals (Cr, Mo, W); Group VIIB metals(Mn, Tc, Re); Group VIII metals (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt);Group IB metals (Cu, Ag, Au); Group IIB metals (Zn, Cd, Hg); Lanthanides(Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu); and Actinides(Th, Pa, U, Np, Pu, Am).
 4. The metallic nanosponges of claim 3, whereinthe metal ions are selected from ions of the group consisting of Cu, Ag,Ni, and Gd.
 5. The metallic nanosponges of claim 3, wherein the metalions comprise copper ions.
 6. The metallic nanosponges of claim 3,wherein the metal ions comprise silver ions.
 7. A metallic nanospongecomprising a plurality of interconnecting, open metal tubes, whereinsaid tubes comprise porous walls, wherein most of said tubes are lessthan about 1 mm in diameter, wherein said porous walls comprise poresbetween about 10 nm and about 1 μm in diameter, and wherein thethickness of said walls is non-uniform, and is between 50 nm about andabout 1 μm.
 8. A metallic nanosponge as recited in claim 7, wherein atleast some of said tubes are 1 mm or longer.
 9. A metallic nanosponge asrecited in claim 7, wherein at least some of said tubes are 1 cm orlonger.
 10. A nanosponge as recited in claim 7, wherein said metal isselected from the group consisting of Group IIA metals (Be, Mg, Ca, Sr,Ba, Ra); Group IIIA metals or semi-metals (B, Al, Ga, In, Tl); Group IVAmetals or semimetals (Si, Ge, Sn, Pb); Group VA metals or semi-metals(As, Sb, Bi); Group VIA semi-metals (Te, Po); Group IIIB metals (Sc, Y,La, Ac); Group IVB metals (Ti, Zr, Hf): Group VB metals (V, Nb, Ta);Group VIB metals (Cr, Mo, W); Group VIIB metals (Mn, Tc, Re); Group VIIImetals (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt); Group IB metals (Cu, Ag,Au); Group IIB metals (Zn, Cd, Hg); Lanthanides (Ce, Pr, Nd, Pm, Sm, Eu,Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu); and Actinides (Th, Pa, U, Np, Pu, Am).11. A nanosponge as recited in claim 7, wherein said metal comprises Cu.12. A nanosponge as recited in claim 7, wherein said metal comprises Ag.13. A nanosponge as recited in claim 7, wherein said metal comprises Pd.14. A nanosponge as recited in claim 7, wherein said metal comprises Pt.15. A nanosponge as recited in claim 7, wherein said metal comprises Ni.16. A nanosponge as recited in claim 7, wherein the diameter of most ofsaid tubes is 500 μm or less.
 17. A nanosponge as recited in claim 7,wherein the diameter of most of said tubes is 50 μm or less.
 18. Ananosponge as recited in claim 7, wherein the diameter of most of saidtubes is 5 μm or less.
 19. A nanosponge as recited in claim 7, whereinthe diameter of most of said tubes is 500 nm or less.
 20. A nanospongeas recited in claim 7, wherein the diameter of most of said tubes is 100nm or less.